#include <iostream>
#include <string>
using namespace std;
int main()
{
    int nums[100005], flags[10005] = {0}, n, flag = 0;
    cin >> n;
    for (int i = 0; i < n; i++)
    {
        cin >> nums[i];
        flags[nums[i]]++;
    }
    for (int i = 0; i < n; i++)
    {
        if(flags[nums[i]] == 1)
        {
            cout << nums[i];
            flag = 1;
            break;
        }
    }
    if(!flag) 
        cout << "None";
    return 0;
}